1. Field of the Invention
The present invention is related to a way of using a magnetic head in a magnetic disk drive, and more particularly, to a magnetic head, which utilizes a magneto-resistive effect-type electromagnetic conversion element, and a magnetic disk drive for reproducing information using this magnetic head.
2. Description of the Related Art
In recent years, a magneto-resistive effect element (MR element) has been utilized in a magnetic disk drive as an element for reproducing magnetically recorded information. An MR element is one that uses changes in resistivity (magneto-resistive effect) corresponding to leakage magnetic fields from a recording medium, and compared to a conventional inductive-type element, has higher reproduction sensitivity, and is not dependent on circumferential speed. In other words, when detecting magnetic changes recorded on a disk medium, which is a recording medium, when using an MR head, detection output does not vary much even if the rotational speed of the disk medium changes. These characteristics are extremely effective for increasing the capacity of a magnetic disk drive and making a disk medium smaller in diameter, and magnetic heads equipped with MR elements are rapidly coming into widespread use now.
FIG. 2 schematically depicts the constitution of an ordinarily used recording medium and the MR element portion of a magnetic head. Most of the area of the MR element 1, which is sandwiched between electrodes 2, is occupied by a single magnetic domain, and when there is no leakage magnetic field from a recording medium 4, either a bias magnetic field is applied, or anisotropy, such that a bias magnetic field exists, is provided so that magnetization occurs in a predetermined direction. This one area is called the magnetically sensitive portion, and by superimposing leakage magnetic fields 6 generated by the recording medium 4, the direction of magnetization is readily rotated from the initial state, and the resistivity of the MR element 1 changes in accordance with the angle of rotation thereof. Therefore, this one area functions effectively for reproducing information, and the width of this area is equivalent to the width of the magnetic head reproduction track.
Shielding layers 3 on both sides of the MR element 1 are arranged for the purpose of enhancing spatial resolution. Even when information is recorded on a recording medium 4 at a high density, it is done so as to prevent the interference of the leakage magnetic fields 6 corresponding to each piece of information, and to enable the separation of each piece of information. The constitution of the MR element portion is as described hereinabove, and even for ones that utilize GMR (giant magnetoresistive effect), which uses a spin-valve system in the magnetically sensitive portion, GMR having a stacked structure, TMR (tunneling magnetoresistive effect) that uses a tunnel junction, or other MR elements, the basic constitution of FIG. 2 is the same.
Because a MR element portion only has a reproduction function and does not have a recording function, by stacking a recording element portion, it can be used as a magnetic head having recording and reproduction functions (composite magnetic head). A rough sketch of a typical constitution of a composite magnetic head is shown in FIG. 3. FIG. 3 is a schematic diagram of the element portion of a magnetic head as seen from the side opposite the disk medium (hereinafter referred to as the medium-opposing side). A magnetic pole 5 for recording is stacked onto the MR element 1.
The recording head of FIG. 3 constitutes an inductive element having magnetic pole 5 and shielding layer 3 as two magnetic poles, and records information to a disk medium via a magnetic field which leaks through a gap portion between magnetic pole 5 and shielding layer 3. Composite magnetic heads, which have MR element 1 as reproduction element as shown in FIG. 3, have rapidly come into use in recent years due to the high reproduction sensitivity thereof, promoting rapid increases in magnetic disk drive capacity.
On the other hand, because a MR element is an extremely thin thin-film element, new problems occur. Ideally it is desirable for the magnetic thin film constituting the magnetically sensitive portion of a MR element to form a single magnetic domain, but there are times when new magnetic domains are formed due to heat, stress or an external magnetic field. A change in magnetic domain structure like this is manifested as a change in reproduction characteristics. Further, when a new magnetic domain is formed, it is often accompanied by Barkhausen noise in the reproduction signal. Consequently, a challenge when using a MR element is giving serious consideration to stabilizing reproduction characteristics while enhancing reproduction sensitivity.
In particular, due to the fact that a composite magnetic head stacks a MR element and a recording element, there are cases in which the recording magnetic field at recording affects the MR element, causing changes in the characteristics of the MR element. With the goal of lessening the influence of a recording magnetic field like this, a structure (piggyback structure) like that shown in FIG. 4, which divides into two the layer that served as both a magnetic pole for the recording head and a shield for the MR element, has come into use recently.
Further, as another method for lessening the influence of a recording magnetic field, a structure, which provides a reproduction element portion outside of a range interposed between two perpendiculars lowered from both ends of the gap-opposing surface of the recording magnetic pole as shown in FIG. 5, is disclosed in Japanese Patent Laid-open No. H11-39619.
As for the relation of the gap between the recording and reproduction heads in the prior art, as shown in FIG. 3, because the structure stacks the MR element and the recording element, there are case when a recording magnetic field affects the MR element, causing changes in the characteristics of the MR element. In response to this, the structures of FIG. 4 and FIG. 5 are proposed as structures for lessening the influence of a recording magnetic field.
The inventors of this application, in order to confirm the effects of these structures, investigated the ratio of reproduction error occurrence when recording and reproducing were repeatedly carried out using magnetic disk drives equipped with composite magnetic heads of the constitutions of FIG. 3 through FIG. 5. The investigation was carried out using 100 magnetic disk drives for each of the magnetic head structures. Each magnetic disk drive was equipped with four magnetic heads, the ambient temperature was 55 C., magnetomotive force at recording was varied from 0.275 AT (ampere-turns) to 0.495 AT, and recording and reproducing were carried out 10,000 times at each magnetomotive force.
FIG. 6 is a comparison of when the magnetic heads shown in FIG. 3 and FIG. 4 were used. In the structure of FIG. 3 (3.0 m-thick recording magneticpole-cum-shield layer), which is the prior art, the ratio of magnetic disk drives, in which errors occurred, suddenly increased in line with increases in the magnetomotive force at recording at 0.385 AT and above, clarifying the effects of magnetomotive force at recording.
Further, according to a study of waveforms at error generation, vertical asymmetry occurred in reproduction waveforms, and Barkhausen noise was confirmed, and the causes of error occurrence are assumed to have been the formation of new magnetic domains in the magnetically sensitive portions of the reproduction elements, and altered bias values.
Conversely, in the structure of FIG. 4 (1.5 m-thick shielding layer, 1.5 m lower magnetic pole, and 0.8 m-thick magnetic separation layer for the shield and lower magnetic pole), the ratio of magnetic disk drives, in which errors occurred, dropped greatly, and the improved efficacy by making the magnetic head the constitution of FIG. 4 is evident.
FIG. 7 compares the structures of FIG. 3 and FIG. 5. The structure of FIG. 3 is the same as above, and in the structure of FIG. 5 (3.0 m-thick recording magnetic pole-cum-shielding layer, distance x from recording magnetic pole=0 m, 0.7 m), the ratio of magnetic disk drives, in which errors occurred, greatly decreased by increasing the distance x, and improved efficacy resulting from the constitution of FIG. 5 is evident.
However, upon studying the results of FIG. 6 and FIG. 7, it was ascertained that errors, albeit few, occurred in both the structures of FIG. 4 and FIG. 5 due to increases in magnetomotive force at recording. This indicates that the effects of a recording magnetic field are exerted across a wide range either by going over the shielding, or via the shielding.
In line with increasing the capacity and density of magnetic disk drives in the future, the reduction of the track width and the reduction of the recording bit length in the circumferential direction will be unavoidable, and as a result of this, it will become necessary to give consideration to thermal demagnetization of the recording medium. Since the coercive force of recording media will be increased even more to prevent thermal demagnetization, greater recording capabilities will be required of magnetic heads. Further, reproduction sensitivity must be heightened even more in order to enhance recording density, and strengthening the stability of the MR element itself will be a substantially difficult task.
A composite head that uses a MR element like this must strive for heightened head sensitivity and enhanced recording capabilities in preparation for future demand for increasing the recording density of magnetic disk drives, but these characteristics will give rise to magnetic instability. Although the structures (FIG. 4 and FIG. 5), which are proposed as measures for improving this, exhibit substantial efficacy compared to a conventional head structure (FIG. 3), they will be inadequate to future increases in magnetomotive force at recording.
In the structure of FIG. 4, this is because increases in the layer thickness of the shields 3 and magnetic pole 3′ will be unavoidable, as a result of which a drop in formatting efficiency is expected in line with increases in the recording and reproduction gaps. In the structure of FIG. 5, this is because an increase in the divergence x between the recording element and the reproduction element will be unavoidable, as a result of which there is concern that performance will decline in line with offset adjustments at recording and reproduction.
An object of the present invention is to provide a magnetic disk drive capable of enhancing the yield of composite magnetic heads while striving to stabilize the performance of the MR element by reducing the influence of a magnetic field at recording, of enhancing the manufacturing yield of magnetic disk drives as a whole by overcoming performance limits resulting from improvement of the head only, and of reducing post-shipment head defects.